1. Field of the Invention
The present invention relates to a collapsible type of zoom lens barrel, used for a camera, which is composed of a plurality of lens barrels, and particularly relates to the zoom lens barrel having a space inside between the lens barrels in which space an electric component such as an electric motor is mounted.
2. Description of the Related Art
Conventionally, there has been provided a collapsible type of zoom lens barrel which has a combination of a plurality of lens barrels, each of which has a cross section, perpendicular to a photographing optical axis, that is generally rectangular in shape, as disclosed in Japanese Laid-Open Patent Publication Nos. 1-130114 and 4-289806. Hereinafter, the lens barrel that is generally rectangular in shape is referred to as a "rectangular lens barrel."
FIGS. 15 to 17 show an example of such a zoom lens barrel which is constituted by telescopically combining three rectangular lens barrels. FIG. 15 is a vertical sectional view which shows the zoom lens barrel in a telephoto state in which the zoom lens barrel projects. FIG. 16 is a partly cut-out view of the zoom lens barrel of FIG. 15, as viewed from a bottom side thereof, and FIG. 17 is a horizontal sectional view of the zoom lens barrel of FIG. 15.
A picture frame 111 is fixed to an inner part of a camera body, and the picture frame 111 is located on a front side (i.e. on a subject side, or on an object side) of a photographing film to be exposed. The picture frame 111 has a rectangular exposure window 112 which leads a light, which has passed through a photographing lens, to the photographing film, which locates on a right side of the picture frame 111 in the figures.
A stationary barrel 120, in which its cross section that is perpendicular to the optical axis (i.e. the photographing optical axis) is formed into a rectangular shape being fitted to the rectangular exposure window 112, is fixed to the picture frame 111. In other words, the stationary lens barrel 120 is immovable relative to the picture frame 111, therefore relative to the camera body.
A movable lens barrel 130 is telescopically fitted to an inside of the stationary lens barrel 120, and the movable lens barrel 130 is driven by a screw bar 113 as shown in FIG. 16 so that the movable lens barrel 130 is projected, or is fed outside, from the stationary lens barrel 120. That is, the screw bar 113 is fixed immovably in the direction of the optical axis, but rotatably, relative to the camera body. In addition, the movable lens barrel 130 has, on its bottom side, a nut portion 131 engaging with the screw bar 113.
In the mechanism, when the screw bar 113 rotates, the movable barrel 130 is moved back and forth in a direction of the optical axis.
In addition, a reference numeral 114 in FIG. 16 denotes a guide bar for guiding a movement of the movable barrel 130 in the direction of the optical axis. More specifically, a sleeve-like member 132, which is fixed to the bottom side of the movable lens barrel 130, engages with the guide bar 114. In addition, a reference numeral 115 denotes a rotation inhibiting bar for preventing the movable lens barrel 130 from rotating about the guide bar 114. An engagement portion 135, which is fixed to a top side of the movable lens barrel 130, engages with the rotation inhibiting bar 115.
On a bottom inner surface of the movable lens barrel 130, is placed a cam plate 150. The cam plate 150 is coupled to the movable lens barrel 130 by a rotational-shaft protrusion 151 which engages with a recessed portion (or concave portion) being provided on the bottom inner surface of the movable lens barrel 130. Therefore, the cam plate 150 is rotatable about the rotational-shaft protrusion 151 on the bottom inner surface of the movable barrel 130. As shown in FIG. 16, a pin 152 is provided near a photographer-side end portion on the cam plate 150. The pin 152 engages with a cam slot 121 which is formed on the bottom surface of the stationary lens barrel 120. In the arrangement, the cam slot 121 inclines with respect to the optical axis. Therefore, when the movable lens barrel 130 moves relative to the stationary lens barrel 120, the cam plate 150 rotates about the rotational-shaft protrusion 151 along with the movement of the movable barrel 130.
Further, near a subject-side (or an object-side) end portion of the cam plate 150, are formed a pair of cam slots 153, 154. These cam slots 153, 154, as will be explained in detail later, have a function to make a first lens group 160 and a second lens group 170 move relative to the movable lens barrel 130, respectively. A movable lens barrel 140 for holding the first lens group 160, and the second lens group 170, are arranged inside the movable lens barrel 130, where the movable lens barrel 140 for holding the first lens group 160 and the second lens group 170 are moved relative to each other in the direction of the optical axis. In addition, the first lens group 160 is fixed within a lens holding circular cylinder (i.e. lens frame) 141 which is fixed to the movable lens barrel 140 for holding the first lens group 160, and the second lens group 170 is fixed within its lens frame 171.
As shown in FIG. 15, a pair of bar-shaped members, namely a guide bar 133 near the bottom side thereof and a rotation inhibiting bar 134 near the top side thereof, are fixed to the inside of the movable lens barrel 130. The guide bar 133 guides a movement of the movable lens barrel 140 for holding the first lens group 160 in the direction of the optical axis, and also guides a movement of the lens frame 171 for holding the second lens group 170 in the same direction.
A sleeve-like member 142 is fixed to the movable lens barrel 140 for holding the first lens group 160, and a sleeve-like member 172 is fixed to the lens frame 171 of the second lens group 170, respectively. Each of these sleeve-like members 142, 172 engages with the guide bar 133. The rotation inhibiting bar 134 inhibits each of the movable lens barrel 140 for holding the first lens group 160 and the lens frame 171 of the second lens group 170 from rotating about the guide bar 133. Namely, an engagement portion 143 is fixed to the movable lens barrel 140 for holding the first lens group 160, and an engagement portion 173 is fixed to the lens frame 171 of the second lens group 170, respectively. These engagement portions 143, 173 engage with the rotation inhibiting bar 134, respectively.
With the arrangement, the movable lens barrel 140 for holding the first lens group 160 and the lens frame 171 of the second lens group 170 are movable back and forth in the direction of the optical axis without rotation.
A pin 144 is fixed on a bottom side of the movable lens barrel 140 for holding the first lens group 160, and a pin 174 is fixed on a lower side of the lens frame 171 of the second lens group 170, respectively, as shown in FIGS. 15 and 16. In the arrangement, the pin 144 of the movable lens barrel 140 engages with the cam slot 153 which is formed near the subject-side end portion of the cam plate 150; meanwhile, the pin 174 of the lens frame 171 engages with the cam slot 154 which is formed also near the subject-side end portion of the cam plate, but is slightly closer to the photographer with respect to the cam slot 153.
As explained above, when the movable lens barrel 130 moves relative to the stationary lens barrel 120, the cam plate 150 rotates in linkage with the movement of the movable lens barrel 130 relative thereto. Because the movable lens barrel 140 for holding the first lens group 160 and the lens frame 171 of the second lens group 170 connected to this cam plate 150 via the pins 144 and 174 respectively, each of the movable lens barrel 140 and the lens frame 171 also moves back and forth respectively in the direction of the optical axis in linkage with the back-and-forth movement of the movable lens barrel 130.
Besides, because the two cam slots 153, 154 are formed so as to have an angle therebetween as shown in FIG. 16, the movable lens barrel 140 for holding the first lens group 160 and the lens frame 171 of the second lens group 170 move in the direction of the optical axis while the relative distance between the movable barrel 140 and the lens frame 171 is changing, thereby achieving an zooming operation of the zoom lens barrel of the camera.
As explained above, each of the three lens barrels 120, 130, 140 has the cross section, perpendicular to the optical axis, that is rectangular in shape; namely, each of the three lens barrels 120, 130, 140 is constructed as the rectangular lens barrel. In the construction, only the stationary lens barrel 120 is positioned permanently immovably relative to the camera body; on the other hand, the movable lens barrels 130, 140 are fed out, or projected, from the front side of the camera. FIGS. 15 to 17 illustrate only the zoom lens barrel, where a broken line "A", designated at a front edge of the stationary lens barrel 120 in the figures, shows an exterior member which locates on a front side of the camera. In the figure, the aforementioned film, which locates on the right side of the frame 111, is designated by an imaginary line.
Now, attention is paid to one, lens barrel located at the forefront of the camera, of the three rectangular lens barrels 120, 130, 140 in FIG. 17. Inside the movable lens barrel 140 for holding the first lens group 160, the lens holding circular cylinder 141 for holding the first lens group 160 is disposed, as described above. There exists a certain space 140a between the movable lens barrel 140 having the rectangular cross section and the lens holding circular cylinder 141 having the circular cross section. This space, although appearing a little bit in FIG. 15 that is the vertical sectional view of the zoom lens barrel, is too narrow to put into effective use. A major part of the space appears in FIG. 17 that is the horizontal sectional view of the zoom lens barrel.
In the arrangement, a miniaturization of a whole body of the camera is realized by mounting a focusing motor 148 for driving a shutter actuator 147 and for driving a focusing mechanism 149 in the space 140a.
However, according to the above mechanism as shown in FIGS. 15 to 17, all the lens barrels 120, 130, 140 for constructing the zoom lens barrel, are composed of the rectangular cylinders (i.e. rectangular lens barrels). Therefore, the space 140a exists necessarily within the movable lens barrel 140, for holding the first lens group 160, which is an innermost movable lens barrel of all the movable lens barrels 130, 140 which are telescopically fitted one over the other. As a matter of course, the movable lens barrel 140 for holding the first lens group 160, when it is in the telephoto state, is located at a position farthest from the camera body (i.e. at a position closest to the subject, or object, to be photographed). Consequently, in case of installing an electric component, such as a motor, inside the space 140a, an electric wire extending from the camera body side cannot help but be relatively longer, in consideration of the relatively longer distance between the camera body and the movable lens barrel 140 locating at the forefront when it is in the telephoto condition. Namely, this arrangement has a disadvantage in view of realization of an effective electrical wiring, or the like.